Make two hacks into one.

* fix stock Android browser behavior of vh units when changing breakpoints
* remove separate CSS content and behavior hacks and merge them into one.
* automatically have buggyfill allow hacks when initializated with 'hacks: window.viewportUnitsBuggyfillHacks' and nothing else (i.e. no 'behaviorHack: true' or 'contentHack: true' is needed anymore).
* fix bug in Opera Mini that messes up nodes using CSS content hack.